Indexing mechanism for machine tools



Sept. 14, 1954 w. RICHTER -INDEXING MECHANISM FOR MACHINE TOOLS Filed Feb. 25, 1946 3 Sheets-Sheet 1 INVENTOR.

Sept. 14, 1954 w. RICHTER INDEXING MECHANISM FOR MACHINE TOOLS 3 Sheets-Sheet 2 gag Mm Filed Feb. 23. 1946 Sept. 14, 1954 W. RICHTER INDEXING MECHANISM FOR MACHINE TOOLS Filed Feb. 23, 1946 3 Sheets-Sheet 3 HHHHHHHHIHHIH\HHlIlIIHlHHIHHHHHHll IHHHHIIIHIHHIHIIIHHII\IIIHHHHIHIIMHHIHH 121 102; #05 /Z5 ZZZ-- Q 5 J Q J 0 11 fi lg F J00 INVEIYTOR.

1 mumm Patented Sept. 14, 1954 UNITED. STATES PATENT OFFICE IND XM NG EGH M. OR MA HI TOOLS William Richter, Kankakee, Ill., a'ssignor toParas mount Textile Machinery 0,0,, Kankakee, 1.11:". a corpor ion o Illinois Application February 23, 1946; Serial No. 64,9,659

14;.Glaims. 1

This invention relates to improvements in indexing mechanism formachine tools, such as milling machines and the like, and its purpose is to provide improved means: for effecting an automatic and accurate relative adjustment of the workand the cutting tool, after each operation of the cutting tool, in order to effect a predetermined spaced relation of the operations on the work. Such indexing operations are useful and important in connection with the cutting of gear teeth, armature slots, the needle slots of knitting machine cylinders and in various other operations where parts formed by successive machine operations are required to have a definite spaced relation.

The principal object of the present invention is to provide improved indexing mechanism of the type referred to in which the spaced relation of successive operations is determined by one or more indexing wheels of relatively large diameter having teeth spaced substantially greater distances apart than the deformations to be formed by the cutting tool, whereby the indexing teeth may be formed with great accuracy and a very precise spaced relation which is reflected in the corresponding but much lesser spacing of the cutting operations; Another object is to provide improved indexing mechanism for machine tools in which the indexing is eifected by a plurality of parallel indexing wheels each provided with accurately formed indexing teeth whichare staggered with respect to the teeth of another wheel, whereby relatively large teeth may be employed and may be arranged so that the feeding mechanism which advances the wheels circumferentially will operate alternately or in succession upon the teeth of; different Wheels, whereby great accuracy is obtained without unduly increasing the size of the indexing wheels. A further object is to provide indexing mechanism comprising a plurality of toothed indexing wheels with pawls for operating them alternately and detents, for holding them stationary during the cutting operations, together with means for automatically operating the detents at. the proper timesto; hold the indexing wheels and to release them and permit. their feeding. movements. Still. another i i t s to pr de improved. saf ty m hanism for a moto riv n. ma hine tool wh y the 2. motor is automatically stepped ii the work table moves more than a predetermined amount in either direction. other objects relate to various features of construction and arrangement which will appear more fully hereinafter. A

The nature of the invention will be understood from the following specification taken with the accompanying drawings in which one embodi merit of the invention is illustrated. In the drawings,

Figure 1- shows a partial side elevation of a milling machine having applied thereto the iiidexing mechanism of the present invention;

Fig; 2 shows a transverse vertical sect-ion taken on the line 2--2- of'Fig. 1;

Fig. 3 shows a transverse vertical section taken on the-line 3 3'of Fig; 1; h

Fig. 4 shows somewhat diagramman cany the electric circuit connections of the switches and solenoids by which the movements of" the-indexing wheels are controlled;

Fig. 5 shows an enlarged s'ide elevation of a portion of an indexing wheel and of the pawl which cooperates therewith, illustrating the formation of the teeth;

Fig. 6 shows an enlarged side elevation of a portion of the teeth of one or the indexing wheels illustrating the cooperation therewith of a switch actuatingroller by which the circuit connections of certain detent operating solenoids are controlled;

Fig; 7 shows an enlarged side elevation of a portion of the mechanism by which the operation of" the driving motor of the machine is arrested in the event that the work table travels too far in either direction;

Fig. 8 shows a partial top plan view and partial section of the switch and lever mechanism by which the operation of the driving motor is arrested at the end of acycl' of operations and also the work table travels mo far in either direction; and.

Big. 9 shows. a somewhat. diagrammatic view of the mechanism illustrated Fig 8 and, the circuit: connection of the electric motor by which the machine is driven.

The inventionis illustrated in the drawing" as being applied to a milling machine of the Gin.- cinnati type manufactured by Qincinnati- Mill,-

the notch 21".

ing & Grinding Machines, Inc, of Cincinnati, Ohio, but it will be understood that it may be applied to various other forms of machine tools where it is desired to effect with accuracy the relative adjustment of the work piece and the tool between successive cutting operations of the tool. The milling machine illustrated in the drawings comprises a bed or base I upon which there is slidably mounted a table II having on its under side a longitudinal extension which engages the undercut groove Ill formed in the base. During the operation of the milling machine the table II is periodically reciprocated longitudinally of the base through mechanism, not shown, which is operated by an electric motor I2 shown diagrammatically in Fig. 9. The table II has mounted thereon a tail stock I3 carrying a tapered center pin I4 which engages an axial recess in one end of an arbor or chuck I5 which carries the work piece I6 clamped between a stationary collar I5 and a detachable collar I5. The other end of the arbor I5 has a central aperture which is engaged by the center point I 1 carried at the end of the shaft I8 which is mounted to revolve in the dividing head 20. This dividing head is secured in adjusted position on the table II by suitable clamping means engaging th longitudinal T-slot I formed therein. The work piece I8 is in the form of a, hollow cylinder, such as the cylinder of a knitting machine, which is adapted to have formed therein a plurality of equally spaced parallel grooves I5 by the relative movement of the work piece with respect to a cutting tool 2| in the form of a milling cutter mounted upon a transverse power driven spindle 22. The table II is adapted to have periodic motion of translation on the base I0 and on each movement thereof toward the left, as viewed in Fig. 1, the cutting tool 2| forms a new slot in the work piece. Between the successive longitudinal movements of the table II the work piece I6 is adapted to be rotated a predetermined extent by the indexing mechanism of the present invention in order to bring about the desired uniform spacing of the grooves I6.

For this purpose the machine is provided with a'pair of indexing wheels 25 of relatively large diameter which are provided with relatively large teeth 25 arranged so that the teeth of one wheel are staggered with respect to the teeth of the adjacent wheel. The two wheels are formed as a part or one unitary construction, being separated from each other by the intervening wheel portion 25 and they are mounted on the shaft I8 to revolve in the direction of the arrow 26. The motion of the indexing wheels is transferred to the chuck or arbor I5 by a split driving block 21 which is clamped on the shank of the arbor I5 by clamping studs 28 and which has anotch 2'! embracing a lug 29 which projects from the face of the adjacent indexing wheel. The driving block 21 may be adjusted in fixed relation to the lug 29 by adjusting screws 30 which pass through the driving block on opposite sides of With this arrangement the motion of the driving wheels is imparted to the chuck or arbor I5 so that when the indexing 'wheel is rotated angularly a distance equal to one-half the length of one of its teeth, a corresponding motion is imparted to the work piece I6.

The indexing wheels are given intermittent motions at the proper times by pawls 32 and 33 which are pivotally mounted upon a bar 34 projecting laterally from the feeding lever 35 which is pivotally mounted upon a bearing at the side of one of the indexing wheels, which bearing is concentric with the axis of the shaft I3 and of the indexing wheels. A pair of coil springs 36, mounted on the bar 34, engage pressure adjusting collars 31 on this bar and press the pawls 32 and 33 against the teeth of the indexing wheels so that the pawls are held under tension in position to engage the teeth of the indexing wheels 25. The pawls are so arranged that when the end of one pawl is in engagement with the substantially radial face of a tooth on one indexing wheel, the other pawl will be riding on the inclined face of the tooth of the other indexing wheel midway between the points of two teeth. With this arrangement, the pawls are adapted to operate alternately on the teeth of the adjacent indexing wheels.

The feeding lever 35 comprises an cuter portion 35 which is adjusted longitudinally on its inner portion 35 through the action of clamping screws 39 engaging elongated slots in the outer portion whereby the effective length of the lever may be adjusted and the pawls 32 and 33 located in the position desired. The lever 35 is normally moved in an upward direction by a coil spring 40 which extends between a screw 4| mounted in the side of the lever and a ring 42 which is secured in the under side of a plate 43 which projects laterally from a rectangular frame member 44 secured to the upper part of the dividing head 20 by studs 45. The extent of the upward movement of the feeding lever 35 is limited by a lug 35 thereon which engages a stop screw 45 secured by a lock nut 41 in the desired adjusted position at the lower end of a bar 48 fixed on the plate 43 and extending downwardly therefrom.

Upon the completion of the reverse stroke of the table II toward the right as viewed in Fig. l, the feeding lever 35 is adapted to be moved downwardly to effect a feeding movement of one of the indexing wheels 25 due to the action of a feeding block or cam 50 carried by a bar 5| which is suspended from a shaft 52 journaled in bearing members 53 secured on the plate 43 by studs 54. This bar 5| is normally moved away from the planes of the indexing wheels by a coil spring 55, shown in Fig. 1, which is connected between a pin on the bar 5| and another pin on the under side of the plate 43, but when the work table II reaches the end of its reverse stroke, with the work piece I6 moved out of engagement with the cutting tool 2|, the lower end of the bar 5| engages an angular stop member 51 detachably secured on a, boss 58 formed on the side of the base I0, thereby rocking the bar 5| and its shaft 52 to cause the feeding block or cam 50 to ride over a feeding roller 60 which is mounted on the upper side of the forward end of the lever 35. The forward lower corner of the member 50 is rounded to permit the ready movement of this member over the roller and this action results in the depression of the feeding lever 35 with the result that one of the pawls 32 or 33 is actuated to feed one of the indexing wheels an angular distance equal to one-half the length of one tooth.

When an indexing wheel 25 has been advanced a distance equal to one-half the length of one of its teeth, it is held in that position during the ensuing cutting operation of the tool 2| brought about by the forward motion of the table II, by

5. one. of the two detents 63 which are mounted. to: slide vertically in a: bracket li l secured to the previously mentionedplate 43, as shown in Figs; 2 and 3. The bracket 64'. supports a housing 65" upon which are mounted: two solenoids 66 and 61. which are associated. through their: detents 63 with the two. indexing wheels 25;. the: solenoid 66 being adapted to operate the detent' for the indexing wheel operated. by the pawl. 32 and. the solenoid 61 is: associated with the detent which engages the; indexing wheel operated byv the pawl 33) Each solenoid has a core 68- which is adapted to be elevated. when the solenoid is energized and this: core" extends into the housing 65 and. is pivotally connected to a lever 69; The lever 69 is pivoted at. an. intermediate point on a bracket secured thehousing and. the: end ofthe lever: opposite the: core or plunger 68 is: pivoted. to the upper end of one. of the detents 63. lever. 69 adjacent its-core or plunger 68? and'the other end of the spring. is fixed to a stationary pin so that the. spring; tends normally to' move the core or plunger 68" downwardly and tomove the associated detent 63 out. of engagement: with the teeth of the indexing wheel. The teeth" of the indexing wheel preferably have the form shown in Fig. 5' whereeach tooth is illustrated as. comprising an inclined front face 25, a comparatively steep rear face 25 and an intermediateinclined face 25' which connects the outer margins of the faces 25 and 25 Each detent 63 is provided with an inclined end face 63 and the sharp tip 63 of adetent is adapted to engage one of the inclined faces 25 when it is lowered and to slide over this face into engagement with. the surface 25 of the teeth so that the indexing wheel is thereby definitely positioned while the relative movement of'the' table ll and the: cutting tool 21 takes place.

In order that the two detents63 may be properly operated in timed relation with the actua-- tion of their indexing wheels 25" under the infiuence of the pawls 32 and 33, the solenoids 66 and 61 are connected: in an electric circuit,

shown diagrammatically in Fig. 4, which is" con-' trolled by two switches 15- and 161. This circuit comprises two terminals 11 and: 18 adapted to be connected to: a" source of supply of. electric current and a conductor 19' leads from one terminal 71 through two'branch conductors 19 to one terminal of each of the two solenoids 66 and 61. The other terminals of. these two solenoids are.- connected by conductors 80 and ill to the terminals of the switch: 16 where they are connected to" the contacts. 82 and 83, respectively; The movable contact 84 of this switch is connected by a conductor 85 to the movable contact.

86. of the other switch 85. This switch has a dead contact 6'! on one side of the movable contact 86 and on the other side of themember 85 there is an active contact 88 which is connected to a conductor 89' leading through the safety switch 90 to the other terminal 18.

As shown in Figs. 1 and 2, the switch 15 is mounted on the under side of an angle bar 91 carried by the bracket 64 and the housing 65'. This switch has an actuating plunger 15*, shown in- Fig. l, which is normally actuated by a spring to move outwardly of the switch casing. The rounded head of this plunger T5 engages an actuating lever 93;, shown in. Fig; 3, which is fixed on the shaft 52 by which. the bar 5.1 is'carried. When the table II reaches the. end of. its reverse stroke; toward. the right as. viewed; in

A coil spring H is attached to each.

6. Fig; l, the engagement of. the lower. end. of: the" bar 5| with. the stop 51 and the: consequent. angular movementrof. the. shaft 521 bringz'about a corresponding angular movement' of. the switch lever 93 so that the plunger [5 moves outwardly and causes the movable. contact: 86 of the switch 15 to engage the dead contact 81, thus opening the circuits of the two solenoids. 66 and 6.1 so that the switch levers. 69 are actuated by their springs I I to move the detents 63 out" of engagement with the. indexing wheels so that. the in dexing wheels may then turn. freely in response to the actuation of. one or the other of the pawls 32 and 33.

As soonas the indexing has. been effected. the: table. II begins its forward stroke,v whereupon the cam carried'by the bar 5| moves out of. engagement withthe roller 60. and. the feeding lever 35 moves upwardly to its normal position determined by the stop member 46. Atthesame time, the bar 5| is restored to. its normal position by the. spring 55., thus causing an angular movement of the shaft 52* so that the switch" lever 93. is operated to push the switch plunger 15 inwardly, thereby causing the movable contact 86. of: the switch to engage thecontactflfl, thus com.- pleting the circuit of one; or the other of the solenoids 66 01161, depending upon the position of'the contactsrof the switch 16.

The switch. 16 is mounted on an inclined bracket. 15 secured by studs 9-6 to the side of the: frame member 44, as shownin Fig; 3, and this switchhas an actuating plunger it. having mounted on the end thereof a roller (5 which is adapted. to ride upon the outer portions. of the. teeth of one of the indexing wheels 25. When the roller H5 is contacting with the tip of a tooth 25, as shown atS'l in Fig. 6, the switch plunger. 16 occupies. a position wherein the movable contact 84 of the switch engages the'st'ationary'contact.82 to complete the circuit of the solenoid 36; and when the roller 16 occupies a position partially be tweentwo. teeth, as shown by dotted lines at. 98 in Fig: 6, the'movable contact 84 of the'switch engages the other stationary contact 83: and compl'etes. the circuit of the other solenoid: 6.1. In this way, the two solenoids 66 and 6 are operated alternately by the switch 16 as the roller 16 a1- ternately engages the tip of the tooth or partially enters. the space between twoteeth during the rotation of an indexing wheel. Thus, when one pawl 32 operates to move one of the indexing wheels 25, the. solenoid 66 is'thereafter operated to cause onev of the detents 63 to engage atooth of' the associated indexing wheel so that this indexing wheel is promptly held in the position to which it has been moved by its pawl 32 and it remains so held in fixed position until the con clusion of both the forward and reverse strokes of the. table I l, whereupon the switch 15 is again actuatedby the. bar 5| to open the circuit of thesolenoid and cause the detent to be restored to its upper position If, on the other hand, the pawl 32 advances its indexing wheel a distance corresponding to one-half the length of one tooth, the roller 16 assumes a position between two of the teeth. 25*, thus moving the contact 84 into engagement. with the other contact 83- and energizing the other solenoid 61' so that'the other'detent 53 then engages a tooth of the indexing wheel which has been. operated by the indexing pawl 33- and. that. indexing wheel held in fixed posi-' tion throughout the forward and reverse strokes of the: table H Inthis way, the roller 16 of the switchlfi; riding ontheteeth ofone of the indexing wheels, effects an automatic closing of the circuit of the appropriate solenoid to cause a detent to engage the teeth of the indexing wheel which has just been operated.

Due to the staggered arrangement of the teeth of the two indexing wheels, one pawl will engage a tooth of one indexing wheel and advance the Wheel a distance equal to one-half the length of a tooth while the other pawl travels idly between the middle point of a tooth and the rear face of the next tooth. On the next stroke of the feeding lever 35, the operations are reversed and the pawl which had an idle motion during the next preceding operation advances the other indexing wheel a distance equal to one-half the length of a tooth. With each such movement of the indexing wheels, the switch operating roller 16' is actuated either by a tip or a depression of one of the indexing wheels to bring about the circuit operations and the alternate operation of the detents which have heretofore been described.

The machine illustrated in the drawings also comprises means for automatically stopping the driving motor by which the table II is moved at the end of a cycle of operations, for example, at the end of the completion of the operation of cutting a complete annular series of longitudinal slots or grooves I6 in the work piece I0. For this purpose, the driving motor I2 is connected in an electric circuit shown in Fig. 9 comprising two conductors I and IOI leading from a source of supply with one of these conductors having connected therein a switch I02 which is adapted to be operated to open the circuit at the end of a cycle of operations and also when there is any excess travel of the table II in either direction. The switch I02 is mounted on the upper part of the U-shaped frame member 44, as shown in Fig. 3, and it has a plunger Ill2 with a contact I03 which is adapted to connect and disconnect the contacts I04 which are connected in the circuit between the motor I2 and the conductor I00. The plunger I02 is provided at its end with tapered surfaces I02 which are adapted to be engaged by the inclined end surfaces I05 formed on a switch actuating pin I05 which is secured to the face of the adjacent indexing wheel 25, as shown particularly in Figs. 3 and 9. At the commencement of the operation upon a particular work piece I6, the indexing wheels are located so that the pin I05 will lie adjacent to the actuating plunger I02 of the switch and then, after a complete revolution of the indexing wheels and a corresponding complete operation on the work piece, an inclined face of the pin I05 will engage the other side of the tapered end of the plunger I02 and thus force the plunger inwardly to disconnect the contacts I04 and thereby open the circuit of the motor I2.

The switch I02 is also employed for the purpose of opening the motor circuit in response to any undue movement of the table I I at the ends of its travel. For this purpose, there is provided a switch operating lever I I 0 which is pivoted by a stud III on the under side of a block II2 which is fixed to the under side of the plate 43, as shown particularly in Figs. 1, 2 and 3. The lever H0 is provided at its end with a pin II0 which en'- gages a recess in the side of the switch plunger I02, as shown in Figs. 8 and 9, and this lever has mounted in a threaded aperture in an intermediate part thereof a horizontally extending threaded actuating rod II4 which is held in ad- Justed position by a set screw H5 and which is adapted, upon extreme movement of the table I I toward the left as viewed in Fig. l, to engage a stationary part IIB of the machine and thereby actuate the lever IIO about its pivot III so that the plunger I02 is thereby operated to open the switch I02. For the purpose of opening the switch I02 upon extreme movement of the table II toward the right, as viewed in Fig. 1, the block H2 is provided with a bracket III having pivotally mounted therein a lever II8 which has a curved lower extremity H8" adapted to engage the side of the lever IIO between its pivot and the switch plunger. The upper end of the lever IIB, above the bracket I I1, is provided with a threaded aperture engaged by another threaded actuating member I20 which is held in adjusted position by a lock nut I2I. The right-hand end of this actuating member I 20 normally does not move into engagement with the upper enlarged part 5| of the rod 5| but if there is an extreme movement of the'table II toward the right, due to a failure of the controlling mechanism to operate properly or for any other reason, the actuating member I20 will engage the part 5| of the bar 5| and rock the lever I I8 about its pivot so that it will actuate the switch lever IIO to open the switch I02 and thereby stop the motor I2.

It will be apparent that the advantages of the invention may be obtained, not only with different forms of machine tools, but also with machines of various sizes, inasmuch as the indexing wheels 25 may be interchanged with other wheels of different diameter or having different tooth formations and the tail stock I3, dividing head 20. driving block 21, and arbor or chuck I5 may be relatively adjusted and interchanged with other parts in order to bring about the desired automatic operation with work pieces of various kinds and sizes.

Although one form of the invention has been shown and described by way of illustration, it will be understood that it may be constructed in various other embodiments which come within the scope of the appended claims.

I claim:

1. An indexing mechanism for machine tools comprising, a pair of toothed indexing wheels arranged to rotate a work piece, the teeth of each wheel being staggered with respect to those of the other wheel, pawls for operating said toothed wheels, and means for operating said pawls to actuate said wheels alternately.

2. An indexing mechanism for machine tools comprising, a pair of toothed indexing wheels arranged to rotate a work piece, the teeth of each wheel being staggered with respect to those of the other wheel, pawls for operating said toothed wheels, and a member carrying both of said pawls and actuated periodically to drive said pawls into alternate engagement with the teeth of said wheels to rotate said wheels step-by-step into successive indexing positions.

3. An indexing mechanism for machine tools comprising, a toothed indexing wheel arranged to rotate a work piece, means including a pawl for intermittently rotating said wheel, a detent adapted to engage said teeth to hold said wheel against rotation, a solenoid for operating said detent, an electric circuit for said solenoid, a switch connected in said circuit, and a cam controlled by said teeth for intermittently actuating said switch thereby to energize said solenoid and intermittently operate said detent into engagement with said teeth.

4. An indexing mechanism for machine tools comprising, a pair of toothed indexing wheels arranged to rotate a workpiece, the teeth of each wheel being staggeredwith respect to those of the other wheel, pawls each positioned for operating a separate'one of said toothed wheels, a common means for operating said pawls to cause them to act alternately to engage the teeth of said wheels, and meansseparate from said pawls for holding each wheel against rotation after the operation thereof-by its pawl.

5. An indexing mechanism for machine tools comprising, a pair, of toothed indexing wheels arranged to rotate a work piece, the teeth of each wheel being staggeredwith respecttothose of the other wheel, pawls each positioned for operating a separate one of said toothed wheels, means for operating said pawls to cause them to act alternately to engage the teeth of said wheels, a pair of detents each adapted to hold one of said wheels against rotation, and cam means actuated by the teeth of one of said wheels for alternately controlling the operation of each of said detents.

6. An indexing mechanism for machine tools comprising, a pair of toothed indexing wheels arranged to rotate a work piece, the teeth of each wheel being staggered with respect to those of the other wheel, pawls each positioned for operating a separate one of said toothed wheels, means for operating said pawls to cause them to act alternately to engage the teeth of said wheels, a pair of detents each adapted to hold one of said wheels against rotation, a pair of solenoids each arranged to actuate one of said detents, an elec tric circuit for said solenoids, and a switch having an operating member riding on the teeth of one of said indexing wheels for closing said circuit to operate one of said solenoids immediately after the associated indexing wheel has been operated by its pawl.

7. An indexing mechanism for machine tools comprising, a pair of toothed indexing wheels arranged to rotate a work piece, the teeth of each wheel being staggered with respect to those of the other wheel, pawls each positioned for operating a separate one of said toothed wheels, means for operating said pawls to cause them to act alternately in rotating said wheels, a pair of detents each adapted to hold one of said wheels against rotation, means for normally retracting said detents from said indexing wheels, a pair of solenoids each adapted when energized to move one of said detents into engagement with the teeth of its indexing wheel, an electric circuit for said solenoids, and a switch having an operating member riding on the teeth of one of said indexing wheels whereby the said circuit is operated to energize said solenoids alternately.

8. An indexing mechanism for machine tools comprising, a pair of toothed indexing wheels arranged to rotate a work piece, the teeth of each wheel being staggered with respect to those of the other wheel, pawls each positioned for operating a separate one of said toothed wheels, means for operating said pawls to cause them to act alternately in rotating said wheels, a pair of detents each adapted to hold one of said wheels against rotation, means for normally retracting said detents from said indexing wheels, a pair of solenoids each adapted when energized to move one of said detents into engagement with the teeth of its indexing wheel, an electric circuit for said. solenoids, a switch having an operating member riding on the teeth of one of said indexing wheels whereby the said circuit is operated to energize said solenoids alternately, and a second switch controlled by each operation of said pawl 10 operating means for opening said circuit preceding each working stroke of one of said pawls and for preparingsaid circuit to be closed by said first named switch after the pawl has operated.

9. An indexing mechanism for machine tools comprising, a. pair of toothed indexing wheels for rotating a work piece, the .teeth of one wheel being staggered with respect to the teeth of the other wheel, a pair of pawls each arranged to engage the teeth of a-separate one of said wheels, and means for actuating said pawls to cause said pawls to act alternatelyto rotate said wheels alternately by increments each equal to one-half the distance between successive teeth on one of said wheels.

10. A reciprocating indexing mechanism for machine tools comprising, a pair of toothed indexing wheels for rotating a work piece, the teeth of one wheel being staggered with respect to the teeth of the other wheel, a pair of pawls each arranged to engage the teeth of a separate one of said wheels, a lever upon which said pawls are mounted, a lever operating cam, and a member carrying said cam and actuated by the reciprocating movement of said mechanism to cause said cam to actuate said lever and said pawls.

11. A reciprocating indexing mechanism for machine tools comprising, a pair of toothed indexing wheels for rotating a work piece, the teeth of one wheel being staggered with respect to the teeth of the other wheel, a pair of pawls each arranged to engage the teeth of a separate one of said wheels, a lever on which said pawls are mounted, a lever operating cam, a member carrying said cam and actuated by the reciprocating movement of said mechanism to cause said cam to actuate said lever and said pawls, means normally retracting said cam carrying member, and means for adjusting the normal position of said cam carrying member.

12. A reciprocating indexing mechanism for machine tools comprising, a pair of toothed indexing wheels for rotating a work piece, the teeth of one wheel being staggered with respect to the teeth of the other wheel, a pair of pawls each arranged to engage the teeth of a separate one of said wheels, a lever having said pawls mounted thereon, a bar suspended from a pivot, a cam mounted on said bar and adapted to move said lever to actuate said pawls, and a stationary stop positioned to be engaged by said bar in response to an overthrow movement of said reciprocating mechanism for rocking said bar about its pivot to control said cam to actuate said lever.

13. An indexing mechanism for machine tools comprising, a toothed indexing wheel arranged to rotate a work piece, each tooth of said wheel having a sharply inclined face and a more gradually sloping face connected by an intermediate inclined face, means for imparting intermittent rotary motion to said wheel, a detent adapted to engage one of said intermediate faces of a tooth and then to move into the space between two of said teeth to position said wheel accurately after rotary motion thereof, and means for actuating said detent.

i l. An indexing mechanism for machine tools comprising, a toothed indexing wheel arranged to rotate a work piece, each tooth of said wheel having a sharply inclined face and a more gradually sloping face connected by an intermediate inclined face, means for imparting intermittent rotary motion to said wheel, a detent adapted to engage one of said intermediate faces of a tooth and then to move into the space between two of detent.

References Cited in the flle of this patent UNITED STATES PATENTS Number Name Date Holz et a1. May 3, 1887 Hilton May 20, 1913 Mitchell Dec. 31, 1918 Soker June 14, 1921 Eisenberg July 2, 1929 Huern Sept. 5, 1933 Number Number Name Date Hill et a1. July 3, 1934 Bennett Sept. 28. 1937 Laessker Jan. 16, 1940 Kriegbaum et a1, July 23, 1940 Coflln et a1. Oct. 15, 1940 Cofln et a1. Oct. 28, 1941 Osplack 0ct.16, 1945 Williams Apr. 19, 1949 Powell Aug. 15, 1952 FOREIGN PATENTS Country Date Great Britain Feb. 26, 1920 

